A wind power plant, or wind park, includes a group of wind turbines that operate collectively as a power plant that generates a power output to a power grid. Wind turbines can be used to produce electrical energy without the necessity of fossil fuels. Generally, a wind turbine is a rotating machine that converts the kinetic energy of the wind into mechanical energy and the mechanical energy subsequently into electrical power.
A wind power plant could also include an energy storage device, such as one or more rechargeable batteries or flywheels, that are also linked to the power grid and that may assist with meeting requirements on the power production by the power plant. When energy demand peaks, the wind turbines of the wind power plant will sink energy directly into the power grid. When energy demand is diminished, excess energy from the wind turbines may be stored in the energy storage device and later discharged to the power grid upon demand to alleviate any deficits in output requirements for the power plant.
The conventional approach is to decide the control actions for the wind turbines independently of the energy storage operating conditions. That is, conventional wind power plant and wind turbine controls are designed to capture as much energy as possible from the wind as long as the stresses on turbine components are acceptable, regardless of the energy storage conditions; e.g., state of charge, remaining life time, etc. Under this conventional approach, the presence of the energy storage device does not have any direct impact on the control decisions for the wind turbines. Charging or discharging of the energy storage device is implemented only after the control actions for the wind turbines are decided.
Stability is a condition of equilibrium between opposing forces. The mechanism by which interconnected synchronous machines maintain synchronism with one another is through restoring forces, which act whenever there are forces tending to accelerate or decelerate one or more machines with respect to other machines. Under steady-state conditions, there is equilibrium between the input mechanical torque and the output electrical torque of each machine, and the speed remains constant. If the system is perturbed this equilibrium is upset, resulting in acceleration or deceleration of the rotors of the machines according to the laws of motion of a rotating body. For a power system with a large penetration of power produced by wind turbine generators or other renewable power sources, there is an increasing demand for providing performance of the wind power plant, so it perform like a regular traditional power plant with synchronous machine. Such a power plant is in the present application called a virtual power plant.